I think hitting kids and the effect really depends on how you do it. I knew people who would hit their kids and look like the devil in the process. THIS DOES NOT WORK!!!
If you treat it as a punishment and not as a way to take out your emotions on how you feel about what the kid did, then it will work. It's just putting heaps of anger in it that will just make the child angrier.
These sorts of punishments are also shorter and the child can reflect on what they did without wasting heaps of time in their room or 'discussing' it with their parents.
Also, kids these days are given to much freedom and choice. Despite thinking this means they can be more independent, inevitably they are relying on the beliefs and choices of people they have spent more time around. If it's not mum and dad, and it's their friends, teachers or friend's parents, they still really have an authority they listen to, just not their parents.
In addition, it's better for mum and dad to teach them than someone else.
DISCLAIMER: Most cases, this whole thing had to be read with the beginning points in mind.